I was curious too so I googled and CNBC says that it’s free because it’s part of a Trump deal that exempts them from tariffs for 3 years and through which they’ll follow Most Favoured Nation pricing for the US

> The biotech company will also offer the first hearing-loss gene therapy for free to eligible U.S. patients following regulatory approval of the product earlier Thursday.

https://www.cnbc.com/2026/04/23/regeneron-inks-drug-pricing-...